In electrophotography, an electrophotographic substrate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging a surface of the substrate. The substrate is then exposed to a pattern of activating electromagnetic radiation, such as, for example, light. The electromagnetic radiation selectively dissipates charge in illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in non-illuminated areas of the photoconductive insulating layer. This electrostatic latent image is then developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image is then transferred from the electrophotographic substrate to a necessary member, such as, for example, an intermediate-transfer member or a print substrate, such as paper. This image developing process can be repeated as many times as necessary with reusable photoconductive insulating layers.
In image-forming apparatus such as copiers, printers and facsimiles, electrophotographic systems in which charging, exposure, development, transfer, etc. are carried out using electrophotographic photoreceptors have been widely employed. In such image-forming apparatus, there are ever-increasing demands for speeding up of image-formation processes, improvement in image quality, miniaturization and prolonged life of the apparatus, reduction in production cost and running cost, etc. Further, with recent advances in computers and communication technology, digital systems and color-image output systems have been applied also to the image-forming apparatus.
Electrophotographic imaging members (photoreceptors) are known. Electrophotographic imaging members are commonly used in electrophotographic processes having either flexible-belt or rigid-drum configurations. These electrophotographic imaging members sometimes comprise a photoconductive layer including a single layer or composite layers. These electrophotographic imaging members take many different forms. For example, layered photo-responsive imaging members are known in the art. U.S. Pat. No. 4,265,990 to Stolka et al. describes a layered photoreceptor having separate photogenerating and charge-transport layers. The photogenerating layer disclosed in Stolka is capable of photogenerating holes and injecting the photogenerated holes into the charge-transport layer. Thus, in the photoreceptors of Stolka, the photogenerating material generates electrons and holes when subjected to light.
More advanced photoconductive photoreceptors containing highly specialized component layers are also known. For example, a multi-layered photoreceptor employed in electrophotographic imaging systems sometimes includes one or more of a substrate, an undercoating layer, an intermediate layer, an optional hole- or charge-blocking layer, a charge-generating layer (including a photogenerating material in a binder) over an undercoating layer and/or a blocking layer, and a charge-transport layer (Including a charge-transport material in a binder). Additional layers such as one or more overcoat layer or layers are also sometimes included.
In view of such a background, improvement in electrophotographic properties and durability, miniaturization, reduction in cost, and the like, in electrophotographic photoreceptors have been studied, and electrophotographic photoreceptors using various materials have been proposed.
Production of a number of arylamine compounds, such as arylamine compounds that are useful as charge-transport compounds in electrostatographic imaging devices and processes, often involves synthesis of intermediate materials, some of which generally are costly and/or time-consuming to produce, and some of which involve a multi-step process. One such intermediate product is the arylamine N,N-di(4-propanoic acid)-4-aminobiphenyl, which is itself useful as a charge-transport compound in electrostatographic imaging devices and processes. Even production of this intermediate compound currently involves a long, costly process.
Currently, arylamine-derivative hole-transporting molecules are prepared by a process that includes reducing or hydrogenating a double bond using compressed hydrogen gas. For example, N,N-di(4-propanoic acid)-4-aminobiphenyl has been produced by selectively reducing N,N-di(4-propenoic acid)-4-aminobiphenyl using compressed hydrogen (H2) gas. While known and useful on a small, laboratory scale, this method is not conducive to large scale production of arylamine-derivative hole-transporting molecules, because it is costly and poses safety concerns.
First, hydrogen gas is a highly diffusible and highly combustible gas. The safety requirements for equipment and facilities for using hydrogen gas are strict, and altering equipment and facilities to meet or exceed the safety requirements for larger scale hydrogenation reactions could be very costly, particularly in light of the small volume necessary for the preparation of arylamine molecules.
Second, the efficiency of conventional hydrogenation reactions using compressed hydrogen gas depends on converting large amounts of the hydrogen gas to the liquid phase. In order to increase efficiency, elevated pressure and temperature, which would require specialized mixing equipment, would be necessary, and would, in turn, increase production costs.
Accordingly, improved processes providing safe, cost-effective and efficient methods for selective hydrogenation are desired for producing arylamines, such as N,N-di(4-propanoic acid)-4-aminobiphenyl, and similar compounds.